Comprehensive and Detailed Explanation From Exact Extract:
To add an existing user (myuser) to an existing group (finance) without removing them from other groups, the correct command is usermod -aG finance myuser. The -aG option appends the user to the supplementary group (s) specified.
Other options:
A). groupadd is for creating new groups, not adding users to groups.
B). groupmod is for modifying group properties, not user membership.
C). useradd creates new users; not applicable to existing users.
Reference:
CompTIA Linux+ Study Guide: Exam XK0-006, Sybex, Chapter 6: " User and Group Management " , Section: " Modifying Group Membership " CompTIA Linux+ XK0-006 Objectives, Domain 1.0: System Management

The .bkp file here is a cpio archive, not a tar or zip. The correct way to extract it is by changing into the target directory (/var/www/html/) and using cpio -idv < /home/dev/web.bkp. The pushd and popd commands ensure the administrator returns to the original directory afterward.

The chage command is used to manage password aging policies, and setting the maximum password age to 90 days enforces the required password change interval for user accounts.

DNS client configuration is a foundational Linux networking task covered in Linux+ V8 system management objectives. When an administrator needs to specify the IP address of a DNS server that the system should use for name resolution, the correct file to modify is /etc/resolv.conf.
The /etc/resolv.conf file defines DNS resolver settings, including one or more nameserver entries that specify the IP addresses of DNS servers. Applications and system services rely on this file to resolve hostnames to IP addresses.
The other options are incorrect. /etc/whois.conf configures WHOIS queries. /etc/nsswitch.conf controls the order of name resolution sources but does not define DNS server IP addresses. /etc/dnsmasq.conf configures a local DNS caching service, not the system-wide resolver directly.
Linux+ V8 documentation highlights /etc/resolv.conf as the authoritative DNS client configuration file, though it may be dynamically managed by tools such as NetworkManager or systemd-resolved.
Therefore, the correct answer is B. /etc/resolv.conf.

Filesystem unmount failures are common troubleshooting scenarios covered in Linux+ V8. When the error
"target is busy" appears, it means one or more processes are actively using files or directories within the mount point.
The correct diagnostic command is lsof | grep /data1. The lsof (list open files) utility displays all open files and the processes using them. Filtering the output with grep /data1 identifies exactly which processes are holding file descriptors on the filesystem, preventing it from being unmounted.
The other options are incorrect. ps -f displays process information but does not show open file usage. du -sh calculates disk usage and does not identify active processes. top monitors system performance but cannot pinpoint filesystem locks.
Linux+ V8 documentation emphasizes using lsof or fuser to identify resource locks before unmounting filesystems. Therefore, the correct answer is D.